The present invention relates to a vehicle speed control method for an automobile, and more particularly relates to a method and apparatus for automatically maintaining the vehicle level at a desired speed without driver operation of the accelerator pedal.
In a conventional vehicle speed control method, the actual running speed of a vehicle at the time when a setting switch is actuated is stored in a storing device, then, the vehicle speed is subsequently compared with the stored vehicle speed to adjust the throttle valve setting in order to maintain the vehicle speed at the stored level. After the desired speed has been set (set operation), the same switch is also used for decreasing the desired vehicle speed (retardation operation) as well as for slightly increasing the desired vehicle speed (increase operation). The particular one of the above-mentioned operations to be selectively carried out depends on the length of time the setting switch is actuated. The increase operation is carried out when the actuation period of the setting switch is shorter than a first interval, the set operation is carried out when the actuation period of the setting switch is longer than the first interval but shorter than a second interval, and the retardation operation is carried out when the actuation period of the setting switch is longer than the second interval.
However, according to such conventional method, the increase operation or the retardation operation may be carried out depending upon the actuation period of the setting switch even when an automatic vehicle speed control operation is to be commenced, and thus the stored vehicle speed may often not be set to a value which is desired by the driver. In other words, the desired vehicle speed at the beginning of the automatic vehicle speed control operation may often vary in accordance with the actuation period of the setting switch.